Field of the Invention
The present invention relates to an input/output structure for connecting an antenna to a dielectric waveguide, and, in particular, to a duplexer used for separating a transmission channel from a reception channel.
Description of the Related Art
There has been a dielectric waveguide duplexer comprising a plurality of dielectric waveguide resonators connected to each other via a coupling window, whereby a resonator group for transmission is combined with a resonator group for reception, in order to transmit and receive only a signal in a desired frequency band via an antenna. Generally, the duplexer is required to comprise an input/output structure having a frequency characteristic of larger bandwidth in order to cover different transmission frequency band and reception frequency band.
FIG. 8 is an exploded perspective view, as fluoroscopically viewed from a lower side, of a conventional dielectric waveguide duplexer comprising an input/output structure of a dielectric waveguide described in JP 2012-147286A.
As illustrated in FIG. 8, a dielectric waveguide duplexer 90 comprises a dielectric waveguide 91a, dielectric waveguide resonators 91b, 91c, 91d, 91e, 91f, and a printed circuit board 99.
Each of the dielectric waveguide 91a and the dielectric waveguide resonators 91b, 91c, 91d, 91e, 91f has an exterior coated with an electrically conductive film 94. The dielectric waveguide resonators 91b and 91c are serially connected to each other via a coupling window 92b exposing a dielectric body, and the dielectric waveguide resonators 91d, 91e and 91f are serially connected to each other via coupling windows 92d and 92e exposing a dielectric body.
The dielectric waveguide 91a and the dielectric waveguide resonator 91b are connected to each other via a coupling window 92a exposing a dielectric body.
The dielectric waveguide 91a and the dielectric waveguide resonator 91d are connected to each other via a coupling window 92c exposing a dielectric body.
The dielectric waveguide 91a has a bottom surface provided with an approximately circular island-shaped electrode 93 that is connected in part to the electrically conductive film 94.
The printed circuit board 99 has a main surface provided with a ground pattern 96 and an approximately circular input/output electrode 95 insulated from the ground pattern 96, and has a rear surface provided with a microstrip line 97. One end of the microstrip line 97 is connected to the center of the input/output electrode 95 via a through-hole 98, and the other end is connected to an antenna or the like via a coaxial connector which is not illustrated.
The dielectric waveguide duplexer 90 is disposed in such a manner that the electrically conductive film 94 and the island-shaped electrode 93 are located in opposed relation to the ground pattern 96 and the input/output electrode 95 of the printed circuit board 99, respectively.
The above described dielectric waveguide duplexer 90 is configured to have a frequency characteristic of larger bandwidth by connecting in part the island-shaped electrode 93 to the electrically conductive film 94 so as to have a C-shaped exposed dielectric portion.